Why do rockets work in space

The train pushes on the track and the car pushes on the road because of friction between the wheels and track or road. However, a rocket in space has nothing to push against. Therefore, the force of propulsion must be something other than friction. The rocket works because of the law of conservation of linear momentum. The law of conservation of linear momentum is very important in physics. Momentum is defined as the mass of an object times its velocity.

Simply stated the conservation law says that in a closed system one without outside influences the total momentum of the system remains constant. Now the momentum of various parts of the system may change, but the total momentum must always be constant.

Consider a machine gun mounted on a lightweight cart. If the gun is fired, the bullets go in one direction while the cart recoils in the other. The magnitude of the momentum of the bullets equals the momentum of the cart but the directions are opposite.

Thus, one momentum is positive and one is negative, making the total change their sum zero. Although things are now moving, the total momentum of the gun-cart system has not changed. In a similar manner, a rocket moves in space because the gases are given momentum as they are expelled by the rocket engine. Consider the rocket resting in space. They just have to take it with them!

On board any rocket a chemical rocket, that is is a fuel tank, an oxidizer tank, and something to spark an explosive reaction in the combustion chamber. Or in the case of a rocket burning hypergols the propellant and oxidizer ignite on contact. Other kids of propulsion harness the same law of physics through slightly different means.

Take ion propulsion for example. An ion engine ionizes propellant by adding or removing electrons to produce ions. Ion engines typically use the gas xenon. The gas is ionized, which sends a steady stream of positively charged ions out the back of the engine. Register or Log In. The Magazine Shop. Rockets are our species' best way of escaping the atmosphere of Earth and reaching space. But the process behind getting these machines to work is far from simple.

Here's what you need to know about getting a rocket into space. Writers and inventors have dreamt of exploring the universe beyond Earth for centuries, but the real challenges of traveling into space only became clear in the 19th century.

Experimental balloon flights showed that Earth's atmosphere thins out rapidly at high altitudes, and so even before powered flight became a reality, engineers knew that devices that create a forward or upward force by pushing against a surrounding medium like air — such as wings and propellers — would be of no use in space. Another problem was that combustion engines — machines such as steam or gasoline engines that generate power by burning fuel in the oxygen from Earth's atmosphere — would also fail in airless space.

Fortunately, a device that solved the problem of generating force without a surrounding medium had already been invented — the rocket. Initially used as weapons of war or in fireworks, rockets generate a force in one direction, called thrust, by the principle of action and reaction: exhaust fumes released by explosive chemicals are pushed out of the back of the rocket at high speed, and as a result the rocket is pushed in the other direction, regardless of any surrounding medium, NASA explains in this primer pdf.

The key to using rockets in space is to carry a chemical called an oxidant that can perform the same role as oxygen in Earth's air and enable the fuel to combust. The first person to seriously study the rocket's potential for space travel, Russian schoolteacher and amateur scientist Konstantin Tsiolkovsky , first published his conclusions in He correctly identified the launch as one of the biggest challenges — the moment where the rocket has to carry all the fuel and oxidant it needs to reach space — as its weight is at a maximum and a huge amount of thrust is needed just to get it moving.

As the rocket gets underway it sheds mass through its exhaust, so its weight is reduced and the same amount of thrust will have a greater effect in terms of accelerating the rest of the rocket.

Tsiolkovsky came up with various rocket designs and concluded that the most efficient setup was a vertically launched vehicle with several 'stages' — each a self-contained rocket that could carry the stages above it for a certain distance before exhausting its fuel, detaching and falling away.

This principle, still widely used today , reduces the amount of dead weight that needs to be carried all the way into space. Tsiolkovsky devised a complex equation that revealed the necessary thrust force needed for any given rocket maneuver, and the "specific impulse" — how much thrust is generated per unit of fuel — needed for a rocket to reach space.

He realized that the explosive rocket propellants of his time were far too inefficient to power a space rocket, and argued that liquid fuels and oxidants, such as liquid hydrogen and liquid oxygen, would ultimately be needed to reach orbit and beyond.

Although he did not live to see his work recognized, Tsiolkovsky's principles still underpin modern rocketry. Rockets must delicately balance and control powerful forces in order to make it through Earth's atmosphere into space. A rocket generates thrust using a controlled explosion as the fuel and oxidant undergo a violent chemical reaction.

Expanding gases from the explosion are pushed out of the back of the rocket through a nozzle. The nozzle is a specially shaped exhaust that channels the hot, high-pressure gas created by combustion into a stream that escapes from the back of the nozzle at hypersonic speeds, more than five times the speed of sound.